Note: Descriptions are shown in the official language in which they were submitted.
~25~ 4
MDF 068 P2 -1-
FLUID JET PRINT ~EAD
Background of the Invention
The present invention relates to the field of jet
drop printing and more particularly to an improved fluid
jet print head and a method of operation therefor.
Jet drop printers operate by generating streams
of small drops of ink and controllinq the deposit of the
drops on a print receiving medium. Typically, the droPs
are electrically charged and then deflected by an elec-
trical field. The drops are formed from fluid filaments
which emerge from small orifices. The orifices may be
formed in an orifice plate which communicate with a flui~
reservoir in which fluid is maintained under pressure.
Each fluid filament tends to break apart at its tip to
form a stream of drops. In order to produce accurate
printing it is necessary that the drops be generated at
accurately timed intervals. This is accomplished by a
process known as "stimulationn.
One prior art approach vibrates the entire print
head, including the ink manifold structure and the oriice
plate structure, together. ~his is shown in Beam e~ al
U.S. Patent No. 3,586,907. Such an arrangement neces-
sarily fatigues the print head mounting structure, since
the mounting structure experiences the same vibrations as
are applied to the manifold and the orifice plate.
Further, tbe amplitude and phase of the vibratory motion
are difficult to control at the frequencies commonly used
for jet drop printer operation.
~25~78~8
MDF 068 P2 -2-
Another prior art stimulation technique, as shown
in Lyon et al U.S. Patent No. 3,739,393, provides the fluid
orifices in a relatively thin, flexible orifice plate. The
orifice plate is stimulated by causing a series of bending
waves to travel therealong. This technique, known as
traveling wave stimulation, results in substantially
uniform drop size and spacing, but the timing of break up
of the fluid filaments varies alonq the length of the
orifice plate.
Other prior art ap~roaches have attempted to
stimulate the filaments in a common phase by excitinq
coplanar movement of the orifices in the ori~ice plate, a
typical example is disclosed in Cha U.S. Patent
4,095,232. Using the technique disclosed in this patent,
stimulators mounted in the upper portion of a fluid
reservoir generate pressure waves which are transmitted
downward through the fluid. Each stimulator includes a
pair of piezoelectric crystals which vibrate in ~hase and
which are mounted on opposite sides of a mounting plate
which is coincident with a nodal plane. A reaction mass
is positioned at the end of each stimulator opposite the
stimulation member. The reaction mass ensures that the
nodal plane is properly positioned.
In British Patent Specification 1,293,980, and
Cha et al U.S. patent No. ~,198,643, print heads are
disclosed in which a pair of piezoelectric crystals are
bonded to opposite sides of a support plate. A print head
manifold structure is bonded to one of the piezoelectric
crystals and a counterbalance is bonded to the other of
the crystals. The weight of the counterbalance is selected
~251~84
MDF 068 P2 -3-
so as to offset the weight of the manifold structure. By
this balanced arrangement, the support plate is placed in
a nodal plane when the two piezoelectric transducers are
energized in synchronism.
s Finally, in Keur U.S. Patent 3,972,474, an ink
drop writing system is shown in which a vibrating nozzle
is used to produce a stream of dro~s. The length of the
nozzle is selected so that its mechanical resonant
fre~uency is much higher than the freauency at which it is
driven. The nozzle, configured as a tube, is surroundeA
by a piezoelectric ring which, when electrically driven,
provides radial contraction and expansion of the tube.
Generally speaking, the prior art stimulation
systems have employed piezoelectric crystals incorporated
into mechanical arrangements of complex acoustical design.
Each such arrangement has had to be individually tailored
for resonant operation at the design freouency within its
specifically associated print head. Such tailoring has
required careful mechanical adjustment and/or trial and
error selection of component parts. This has "tuned" the
stimulation system for operation within an extremely narrow
range of operating frequencies. For operation outside this
range the performance is extremely degraded.
In some applications it is desirable to adjust the
frequency of the stimulation driving signal. A typical
example is in precision printing of high resolution
graphics. In such printing there are unavoidable varia-
tions in the transport speed of the substrate, and these
variations tend to produce drop positional placement
~25(~7~
MDF 068 P2 -4-
errors. This can be corrected by adjusting the stimula-
tion drive, as shown for instance in Van Brimer et al U.S.
Patent 3,588,906. This results in stimulation at a
frequency which deviates from the nominal design frequency.
Such deviation cannot be accomodated satisfactorilv by
systems of the above described types.
Thus it is seen that there is a need for an
improved and simplified apparatus for effectlng fluid jet
stimulation and for accommodating adjustments in the
lo frequency of the stimulation~
Summary of the Invention
The present invention provides constructions for
simpler and more effective stimulation of fluid ~et ~rint-
ing streams. Moreover the invention is applicable to
multi-orifice print head systems of the type wherein an
orifice plate is excited by traveling bending waves as
well as those wherein the orifice plate is excited for
movement with its orifices coplanar. In either case the
system may be provided with stimulation means comprising a
high acoustic Q solid member having a major dimension
substantially equal to an integral number of half wave-
lengths of vibration at the stimulation fre~uency and two
other minor dimensions each substantially shorter than a
half of such a wavelength. A pair of elongated strips of
piezoelectric material are bonded to opposite surfaces of
the metallic member and driven so as to elongate periodi-
cally at the stimulation frequency in a direction parallel
to the major dimension of the high Q member. This induces
corresponding shear stresses in the surfaces of the metal-
lic member, and those shear stresses cause the desired
vibration of the orifice plate.
~25~84
MDF 06~ P2 -5~
For application to traveling wave stimulation the
metallic member may comprise a rod-like structure supported
for localized contact against the orifice plate. For
coplanar orifice movement the high ~ member may comprise
support structure integrally associated with the print
head body.
In one aspect the present invention provides an
improved fluid jet print head comprising an elongated
print head body, the length or major dimension of the body
between first and second ends thereof being substantially
greater than its other minor dimensions. The body defines
a fluid receiving reservoir in its first end and at least
one orifice communicating with the fluid receiving reser-
voir. Fluid is supplied to the reservoir under pressure
by appropriate means such that it emerges from the reser-
voir to form a fluid stream. A transducer means is mounted
on the exterior of the body and extends along the body in
the direction of elongation toward both the first and
second ends of the body. The transducer means is respon-
sive to a stimulation driving signal for changing dimension
in the directlon of elongation of the body, thereby causing
mechanical vibration of the body and break up of the fluid
stream into a stream of drops. The major dimension of the
print head is substantially equal to an integral number of
half wavelengths of head vibration at the frequency of the
stimulation driving signal.
The transducer means comprises a pair of elon-
gated strips of piezoelectric material bonded to opposite
sides of the body and extending in the direction of
elongation. The piezoelectric strips induce alternating
shear stresses in the surfaces of the elongated print head
lZ~
MDF 068 P2 -6-
body in the direction of elongation of the body. These
surface shear stresses are converted into compression
waves which travel in the direction of elongation and
produce longitudinal vibration of the print head body at
the stimulation driving freguency.
The transducer means further comprises means for
electrically connecting the pair of transducers in paral-
lel, whereby the transducers operate in phase ~o as to
produce vibration which is in a direction substantially
parallel to the direction of elongation of the elongated
print head body. A support means for the print head
engages the print head body intermediate and substantially
equidistant from its first and second ends.
Alternatively, the transducer means may comprise
means for electrically connecting the transducers so that
they operate out of phase, thus producing flexure waves.
The support means for the print head engages the print
head body a distance from each end of the body approxi-
mately equal to 23 percent of the overall length of the
body.
The print head is provided with a fluid receiving
reservoir and an orifice plate having a plurality of
orifices communicating with the reservoir. The orifice
plate may be mounted upon a face of the print head extend-
ing perpendicular to the major dimension of the head or,
alternatively, upon a face extending parallel to the major
dimension. Accordingly, the printing jets may be directed
either parallel or perpendicular to the major dimension of
the print head.
)784
MDF 068 P2 -7-
The fluid jet print head may further include means
for applying an electrical driving signal of a frequency
substantially equal to fO = C/2L, where L is the dimen-
sion of the body in the direction of elongation, and C is
the speed of sound through the body~ In this case the
fluid jet print head is driven at a frequency approxi-
mating its mechanical resonant frequency.
For flexure wave vibration, the transducers are
driven at a frequency Fo - a Ca/L2, where a is the
transverse thickness of the print head body and ~ - l in
MKS units. In this case, two nodal mountinq axes are
established a distance equal to approximately .23 of the
length of the print head body, centered between the
transducers.
The method for stimulating the break up of a
fluid stream emanating from at least one orifice communi~
cating with the fluid reservoir in a half wavelength fluid
jet print head includes the steps of:
(a) providing an elongated print head which
defines the reservoir and orifice at one
end thereof;
(b) applying fluid under pressure to the reser-
voir so as to produce fluid flow through
the orifice;
(c) supporting the print head at points in a
plane substantially equidistant from the
ends of the elongated print head and normal
to the direction of elongation of the print
head; and
~25()~7~3~
MDF 068 P2 -8-
(d) alternately elongating and contracting the
print head substantially at the resonant
frequency of the print head, whereby the
print head is supported in at least one
nodal plane and the stream is effectively
stimulated to break up into drops.
The resonant frequency of the print head may be
substantially equal to the resonant frequency of the fluid
stream. The print head may be elongated and contracted by
means of piezoelectric transducers bonded to its exterior.
The stream may also be stimulated by operating
the transducers out of phase, thereby causing flexure of
the print head. In this stimulation mode, the print head
is mounted at points spaced from the ends by a distance
approximately equal to 23 percent of the length of the
print head when operated in its fundamental bending mode.
In another aspect the invention provides improved
traveling wave stimulation through use of an elongated
stimulator member having a length which is substantially
greater than its other dimensions and a pair of transducer
means mounted on opposite exterior sides of the stimulator
member. The transducer means extend in opposing relation
a substantial distance in the direction of elongation of
the stimulation member and are responsive to an electrical
driving signal for applying surface shearing stresses to
the stimulation member in the direction of elongation.
In yet another aspect the present invention
provides improved contructions for detecting the frequency
and amplitude of print head stimulation for use in print
head control.
~Z5~7~
MDF 068 P2 -9-
Accordingly, it is an object of the present inven-
tion to provide improved apparatus and method for fluid
jet stimulation wherein a pair o transducers are mounted
on opposite surfaces of a metallic member and are excited
to produce surface shearing stresses and consequential
vibration of an orifice plate through which a fluid jet is
being directed.
Other objects and advantages of the invention will
be apparent from the following description, the accompany-
ing drawings and the appended claims.
Brief Descri~tion of the Drawings
Fig. 1 is an exploded view, illustrating a first
embodiment of the fluid jet print head of the present
invention;
Fig. 2 is a plan view of the print head of Fiq.
1, with the orifice plate removed;
Fig. 3 is a side view of the print head of Fig. 1
with the electrical drive circuitry illustrated;
Fig. 4 is an enlarged partial sectional view,
ta~en generally along line 4-4 in Fig. 2;
Fig. 5 is a graph, useful in explaining the
operation of the print head of the present invention;
Fig. 6 is a second graph, useful in explaining
operation of the print head of the present invention.
Fig. 7 is a schematic diagram illustrating driving
cixcuitry for the fluid print head.
Fig. 8 is a side view of a second embodiment of
the fluid jet print head of the present invention; and
Fig. 9 is a perspective view of a third embodi-
ment of the fluid jet print head of the present invention.
~L2S~
MDF OÇ8 P2 -10-
Fig. 10 is a perspective view of a fourth embodi-
ment of the print head and stimulator of the present inven-
tion, with portions broken away to reveal interior struc-
ture;
Fig. 11 is a sectional view of the stimulator of
Fig. 10, taken through the center of the stimulator in a
plane parallel to the axis of elongation thereof;
Fig. 12 is a sectional view taken generally along
line 12-12 in Fig. 11: and
Fig. 13 is an enlarged perspective view of a
fifth embodiment of the present invention, with portions
broken away and in section.
Detailed Description of the Preferred Embodiments
A first embodiment of the print head of the
present invention is shown in Figs. 1-4. ~he print head
generally includes an elongated print head body 10, having
a major dimension or length, L, which is substantially
greater than its other dimensions a and b. The body 10
includes an orifice plate 12 bonded to a block of high
acoustic Q solid material 14. The body 10 defines a fluid
receiving reservoir 16 in its first end, and at least one
and preferably a number of orifices 18 which are arranged
in a row across orifice plate 12. Block 14 is preferably
manufactured from stainless steel, but other high acoustic
Q solid materials such as glass or ceramic may be used.
Block 14 defines a slot 20 which, in conjunction with
orifice plate 12 defines the reservoir 16. The block 14
further defines a fluid supply opening 22 and a fluid
outlet opening 24, both of which communicate with the slot
20.
MDF 068 P2
The print head further includes means for supply-
ing fluid to the reservoir 16 under pressure such that
fluid emerges from the orifices 18 as fluid filaments
which then break up into streams of drops traveling in a
direction parallel to the major dimension of the body 10.
A pump 26 receives fluid from a tank 28 and delivers it,
via fluid conduit line 30, to the reservoir 16. A conduit
32 is connected to fluid outlet 24 such that fluid may be
removed from the reservoir 16 at shut down of the print
head or during cross-flushing of the reservoir 16. As
will become apparent, the end of the print head to which
conduits 30 and 32 are attached, as well as the opposite
end of the print head, is subjected to mechanical vibra-
tions which cause the fluid filaments to break up into
streams of drops of uniform size and spacing. The conduits
30 and 32 are selected from among a number of materials,
such as a polymeric material, which have a vibrational
impedance substantially different from that of the stain-
less steel block 14. As a consequence, power loss through
the conduits 30 and 32 and the resulting damping of the
vibrations are minimized. The ink conduits may also be
machined to the nodal plane, where vibrations are minimal
and can then be connected to tubes having less critical
acoustic properties.
The print head further includes support means,
such as mounting flanges 34. Flanges 34 are relatively
thin and are integrally formed with the block 14. The
flanges 34 extend from opposite sides of the elongated
print head body 10 and are substantially equidistant from
the first and second ends of the body. As a result, the
Elanges may be used to support the body 10 in a nodal
plane. The flanges 34 are therefore not subjected to
substantial vibration.
~250`;t~
MDF 068 P2 -12-
The print head further comprises a transducer
means, including thin piezoelectric transducers 36 and
38. The transducers are bonded to the exterior of the
body of block 14 and extend a substantial distance along
the body in the direction of elongation thereof, from
adjacent the support means toward bo~h the first and second
ends of the body. The transducers 36 and 38 respond to an
electrical driving signal, provided by power supply 40 on
line 42, by changing dimension, thereby applying shear
stresses to the surfaces of the print head body. Due to
the geometry of ~he print head body these shear stresses
are converted into compression waves which travel along
the body in a direction parallel to the direction of extent
of the major axis. The resulting compression waves stimu-
late the fluid streams to break up into streams of drops.
The piezoelectric transducers 36 and 38 have elec-
trically conductive coatings on their outer surfaces, that
is the surfaces away from the print head block 14, which
define a first electrode for each such transducer. The
metallic print head block 14 typically grounded, provides
the second electrode for each of the transducers. The
piezoelectric transducers are selected such that when
driven by an A.C. drive signal, they alternately expand
and contract in the direction of elongation of the print
head. As may be seen in Fig. 3, transducers ~6 and 38 are
electrically connected in parallel. The transducers are
oriented such that a driving signal on line 42 causes them
to elongate and contract in unison.
If desired, an additional piezoelectric transducer
44 may be bonded to one of the narrower sides of the print
head to provide an electrical output potential on line 46
- 3L2~{~ Y~3~
MDF 0~8 P2 -13-
which fluctuates in correspondence with the elongation and
contraction of the print head block 14. The amplitude of
the signal on line 46 is proportional to the amplitude of
the mechanical vibration of the block 14.
The mechanism by which the first embodiment of the
print head of the present invention functions may be
described as follows. The elongated print head body is
somewhat analogous to an ordinary helical spring. If such
a spring is compressed and then quickly released, it will
oscillate about its center at a frequency fO, called its
fundamental longitudinal resonant frequency. In this
condition, both ends of the spring move toward and away
from the center of the spring, while the center remains at
rest. Therefore, if one fixes the center of the ~pring
and repeats the above described operation, the spring will
oscillate in the same manner at the frequency fO.
The steel block 14 which forms a part of the print
head body can be considered to be a very stiff sPring. If
properly mechanically stimulated, it may therefore be held
at its center, as by flanges 34, while both ends of the
block 14 alternately move toward and away from the center.
Since the center of the block lies in a nodal plane, the
flanges 34 are not subjected to substantial vibration and
the support for the print head does not interfere with its
operation. As ~he end of the print head body 10 which
defines the fluid receiving reservoir 16 is vibrated, the
vibrations are transmitted to the fluid filaments which
emerge from the orifices 16, thus causing substantially
simultaneous uniform drop break up. Note that the reser~
voir 16 is small in relation to the overall size of the
block 14 and is centered in the end of the block. As a
MDF 068 P2 14-
consequence, the reservoir 16 does not interfere signifi-
cantly with the vibration of the block 14, nor affect the
resonant frequency of the print head substantially. The
homogeneous nature of the solid block assures uniform
amplitude of vibration along the ends whereby synchronous
breakup of relatively long, dense ink Jet arrays is
possible.
The fundamental resonant frequency of the block
14 can generally be said to be given by
l fo = C/2L = ~ /2L
where C is the speed of sound through the print head block
14 material, L is the length of the print head body in the
direction of elongation, E is the modulus of elasticity of
the material forming block 14 and is the density of the
material forming the block 14. Preferably the print head
is designed to operate at or near its resonant fre~uency,
and this frequency, in turn, is selected within an appro-
priate fluid jet stimulation frequency range, e.g., 50KHz
to lOOKHz; that is, the print head block is constructed of
a material and with dimensions such that its fundamental
longitudinal mode resonant frequency is approximately equal
to the nominal jet droplet stimulation frequency for the
printing system. The homogeneous nature of the solid block
assures uniform amplitude of vibration along the ends
whereby s~nchronous breakup of relatively long dense ink
jet arrays is possible. As above described, print head
block 114 has a length L which is equal to a half wave-
length, where a wavelength is a distance determined by the
equation:
fo
~L25~
M~F 068 P2 -15-
In general L may have a value substantially equal to any
integral number of half wavelengths. Thus:
L = n ~
By providing a pair of pie~oelectric transducers
36 and 38 on opposite sides of the block 14, the block 14
is elongated and contracted without the flexure oscilla-
tions which would otherwise result if only one such piezo-
electric transducer were utilized. Additionally, the use
of two piezoelectric transducers allows for a higher power
input into the print head for a given voltage and, conse-
quently, for a higher maximum power input into the print
head, since only a limited voltage differential may be
placed across a pie~oelectric transducer without break
down of the transducer.
As is well known, E, p and L are temperature
dependent and, as a consequence, the resonant frequency of
the print head varies with changes in temperature. The
variation ~f in fO for a temperature change of Q T, at or
near room temperature, is given by ~ f = ~fok~T/2~ where
k is approximately 4 x 10-4/C for stainless steel.
When the dimensions a and b are small as compared
to L, the print head can be driven at a frequency off
resonance. Fig. 5 illustrates the changes in the driving
voltage applied to the transducers which are required in
order to drive a single jet print head for a constant
nominal filament length of 16.5 x 10 3 in. In general,
the nominal filament length is a function of both the
driving voltage and the driving frequency~ At any given
driving frequency the nominal filament length decreases
with increases in the driving voltage.
$2~
MDF 068 P2
From Fig. 5, it is clear that at resonance, 83
KHz, the print head requires a drive voltage of approxi-
mately 20 volts peak-to-peak. When driven by an oscil-
lator at a frequency to either side of the resonant
frequency, the driving voltage must be increased substan-
tially in order to maintain the filament length at 16.5 x
10-3 in. On either side of the resonant frequency, the
voltage required rises approximately linearly with
frequency. There is, however, a maximum voltage which may
be applied to the piezoelectric transducers and, so lon~
as the maximum voltage is not exceeded, the transducers
may be driven on the positive slope portion of the curve
of Fig. 5, or the negative slope portion of the curve.
Assuming that the resonant frequency remains constant, the
driving frequency may be varied in synchronization with
fluctuations in speed of the print receiving medium upon
which drops from the print head are to be deposited,
thereby compensating for such fluctuations. In such an
instance, the frequency of the drive signal is monitored,
however, and the voltage of the drive signal adjusted
accordingly in order to compensate for the frequency shift
and thereby maintain the desired fluid filament length.
If desired, the additional piezoelectric trans-
ducer 44 may be utilized to monitor the frequency of the
drive signal and amplitude of vibration of the print head
and provide a corresponding feedback signal. This feed-
back signal is plotted in Fig. 6 as a function of the
frequency of the driving signal for the maintenance of a
single jet print head nominal fluid filament of a length
equal to 16.5 x 10-3 in., and a diameter of approxi-
mately 1 x 10 3 in. Assuming no change in the resonant
~2~
MDF 068 P2 -17-
frequency of the print head or the jetr a fluid filament
of a desired length can be maintained by monitoring the
output voltage and frequency on line 46 and adjusting the
level of the driving signal as needed to maintain the
output voltage on line 46 at a reference voltage level
specified by the curve of Fig. 6.
In a typical application it may be desirable to
apply in the order of about 2 percent fre~uency adjustment
to the stimulation driving signal. In order to accommo-
date this, the minor dimensions of the print head prefer-
ably should be less than about one-fourth the major
dimension, and the major dimension should be substantially
equal to an integral number of half wavelengths at the
driving frequency.
It will be appreciated that numerous variations
may be made in the disclosed print head within the scope
of the present invention. For example, flanges 34 may be
deleted. Another arrangement, such as support screws may
be provided for attaching the print head body to appro-
priate support str~cture, as long as the point or points
of attachment lie substantially in the nodal plane inter-
mediate the ends of print head body 10. Alternately ink
supply tubes may serve as support members when connected
to fluid conduits internal to the block extending from the
ink reservoir to the nodal plane.
Reference is made to Fig. 7 which illustrates a
circuit which may be used for supplying a fixed frequency
stimulation driving signal. The output of a fixed
frequency oscillator 48 is supplied to transducers 36 and
38 via a voltage controlled attenuator circuit 50, a power
amplifier 52 and a step-up transformer 54. The output
~ `7~-~
MDF 068 P2 -18-
from transducer 4~ on line 46 is used to control the amount
of attenuation provided by circuit 50. The signal on line
46 is amplified by amplifier 56, converted to a D.C.
signal by converter 58, and then compared to a selected
reference signal by summing circuit 60 to produce a signal
on line 62 which controls the attenuation provided by
circuit 50. By this feedback arrangement, the amplitude
of the mechanical vibration of the print head is precisely
controlled. For variable frequency stimulation a somewhat
different stimulation driving circuit may be employed.
Fig. 8 is a side view illustrating a second
embodiment of the present invention, with elements corres-
ponding to the print head of Fig. 1 being labeled with
identical reference numerals. In this embodiment the
transducers 36 and 38 are oriented on the print head body
such that a positive driving signal on line 42 causes one
of the transducers to elongate and the other transducer to
contract, while a negative driving signal has the opposite
effect. As a conseguence, as an A.C. driving signal is
supplied to line 42, the print head is caused to vibrate
in its first flexure mode. This vibrational mode is
illustrated in Fig. 8 by medial lines 64 which, although
greatly exaggerated in flexure for purposes of clarity,
indicate the extent of movement of the center of the print
head body 14. It should be noted that lines 64 cross at
points which are approximately o23L inward from each end
of the print head body, thus indicating nodal points.
Mounting holes 66 are drilled into body 1~ at the nodal
points and a second corresponding pair of mounting holes
are drilled into the opposite side of the print head
body. By providing mounting pins which extend into holes
66, pivot supports are provided which do not interfere
with flexure of the print head.
~2~ 3
MDF 068 P2 -19-
This flexure mode may be excited by driving the
transducers at a frequency
fO -- aCa/~2, where ~ is approximately 1 in
MKS units.
This is a simplification of the resonant frequency equation
fo - 9~CK/8L2, where K is the radius
of gyration, which ~or
the print head illus-
trated equals a/2.
A third embodiment of the invention, as illus-
trated in Fig. 9, comprises a fluid jet print head 110
having a major dimension L and minor dimensions a and b
corresponding to like designated dimensions for the embodi-
ment of Fig. 1. Similarly, fluid jet p-int head 110 has a
fluid receiving reservoir 116 provided with a supply open-
ing 122 for reception of printing fluid from a fluid
conduit 1300 A fluid exit conduit 132 enables fluid
removal from the print head.
Print head 110 also has an orifice plate 112
provided with a series of orifices 118 in communication
with reservoir 116 but mounted differently than the corres-
ponding orifice plate 12 of print head 10. As illustrated
in Fig. 9, orifice plate 112 is mounted on a side face of
print head 110 covering a sidewardly extending slot 120,
so as to produce a series of jets 150 projecting in a
direction perpendicular to the major dimension of the
print head. These jets may be selectively charged by a
series of electrodes 152, as is well known in the art.
Stimulation of jets 150 is achieved by applying
stimulation driving signals of appropriate frequency to a
pair of piezoelectric transducers 136, 138 bonded to the
~LZ~
MDF 068 P2 -20-
narrow sides of print head 110. The stimulation mechanism
is the same as for the embodiment of Fig. 1. A stimulation
driver (not illustrated) applies driving signals at near
resonant frequency in common phase to both of transducers
136, 138. The transducers lengthen and shorten in unison,
thereby applying shearing stresses to the surface of the
print head. These stresses extend in a direction parallel
to the major dimension of the print head and are converted
to compression waves traveling in that dlrection. In
order to minimi2e the power required for stimulation
orifice plate 112 preferably should be located near the
end of print head 110, as illustrated. Furthermore, the
major dimension should again be substantially equal to an
integral number of half wavelengths at the stimulation
frequency, and the minor dimensions preferably should be
less than about one-fourth the major dimension.
Print head 110 also may be provided with a pair
of mounting flanges 134, 134 positioned for providing
support at a nodal plane. A feedback transducer in the
form of a strip of piezoelectric material 144 may be
mounted on print head 110 as illustrated. Electrical
connections to transducers 136, 138 and 144 may be made as
shown in Fig. 7 for transducers 36, 38 and 44 respectively.
Figs. 10, 11 and 12 illustrate a fluid jet print
head and stimulator therefor constructed according to a
fourth embodiment of the present invention. The print
head includes a manifold means consisting of an upper mani-
fold element 210, a lower manifold element 212, and a
gasket 214 therebetween. The manifold means defines a
fluid receiving reservoir 216 to which fluid may be applied
under pressure via fluid inlet tube 218. Fluid may be
~2~
MDF 063 P2 -21-
removed from reservoir 216 through outlet tube 220 during
cleaning operations or prior to extended periods of print
head shutdown.
An orifice plate 222 is mounted on the manifold
means. The plate is formed of a metal material and is
relatively thin so as to be somewhat flexible. Orifice
plate 222 is bonded to the manifold element 212, as for
example by solder or by an adhesive, such that it closes
and defines one wall of the reservoir 216. Orifice plate
222 defines a plurality of orifices 224 which are arranged
in at least one row and which communicate with the reser-
voir 216 such that fluid in the reservoir 216 flows through
the orifices 224 and emerges therefrom as fluid filaments.
A stimulator means 226 mounted on contact with the orifice
plate 222 vibrates the orifice plate to produce a series
of bending waves which travel along the orifice plate 722
in a direction generally parallel to the row of orifices.
The stimulator means 226 includes a stimulator
member 228, configured as a thin metal rod. The type of
metal for the stimulator member 228 is selected to be
compatibl~ with the fluid supplied to reservoir 216. How-
ever, member 228 need not be made of metal, as other high
aco~stic Q solid materials such as glass or ceramic could
be used. The stimulator member 228 is of a length L which
is substantially equal to an integral number of half wave-
lengths of an acoustic wave traveling along the stimulator
member 228. The distance ~ may be calculated by the
formula set forth above in connection with the description
of the embodiment of Fig. 1.
T~le end 230 of member ~28 is tapered so that the
member 228 contacts the orifice plate 222 in a localized
region which is substantially a point. As is known, such
~.25~
MDF 068 P2 -22-
point contact on the center line of the orifice plate 222
insures that bending waves of a first order are generated
in the orifice plate 222, and that satisfactory stimula-
tion is obtained.
The stimulator means 226 further includes piezo-
electric crystal means, comprising piezoelectric crystals
232 and 234, which are mounted on the stimulator member
228. The crystals 232 and 234 each include a thin, elec-
trically conductive layer on their outer surfaces to which
conductors 236 and 238 are electrically connected. The
inner surfaces of the crystals are in contact with and are
grounded by the member 228. Member 228, in turn, may be
grounded through orifice plate 222 or through ground
conductor 240. The crystals 232 and 234 are configured
such that they tend to compress or extend in a direction
parallel to the axis of elongation of the member 228 when
a fluctuating electrical potential is placed across the
crystals. As a consequence, when an A.C. electrical drive
signal is applied to lines 236 and 238 by driver circuit
means 240, the crystals 232 and 234 produce acoustic waves
in the stimulator member 228. The circuit 240 supplies an
electrical drive signal at a frequency fO, as specified
above in relation to the length of the member 228.
In the embodiment illustrated in Figs. 10-12, the
stimulator member is substantially equal in length to one
wavelength, that is, n is equal to 2. The member 228
extends into the manifold means through an opening 244
defined by element 210. The member 228 contacts the
orifice plate 222 inside the reservoir 216. A seal, such
as O-ring 246 surrounds the member 228, contacting the
member 228 and element 210.
. 2~5U~
MDF 068 P2 -23-
The stimulator means is mounted by tapered pins
248 which engage generally conical detents 250 in the sides
of member 228. The pins 248 and detents 250 provide a
pivotal mounting which restricts movement of member 228
vertically. As may be noted, the detents 250 are posi-
tioned 1/4 ~ from the upper end of the member 228, as seen
in Fig~ 11, while the O-ring 2~6 contacts the member 228
substantially 1/4 ~ from the lower end of the member 228.
It will be appreciated that since crystals 232 and 234
extend above and below the detents 250 by substantially
equal distances, pins 248 support the stimulator means in
a nodal plane. Since the ring 246 contacts the member 228
1/2A below the pins 248, O-ring 246 also contacts the
member 228 at a nodal plane. Thus substantial damping
between the member 228 and the ring 246 does not occur.
Additionally, the end of 230 of the member 228 is 1/4~
below a nodal plane and therefor at an anti-node, producing
maximum amplitude mechanical stimulation for generation of
the bending waves in the orifice plate 222. It will be
understood that it is desirable to limit the length Lc
of the crystals 232 and 23~ to 1/2~ or less. If the length
of the crystals is greater than this, their vibratory
motion will tend to counteract formation of standing waves
in the member 228 and the production of nodal planes.
It will be appreciated that member 228 could be
substantially longer than illustrated. The length of the
member can be increased in multiples of 1~2 wavelength
with predictable harmonic progressions. In any eventj
however, it is desirable that the mounting for the member
228 be at a nodal plane and that sealing also occur at a
nodal plane so that vibrational energy is not lost through
the sealing or the mounting structures and that the member
228 contacts the orifice plate 222 at an anti-node.
~.2SS~7~3~
MDF 068 P2 -24-
An additional pair of piezoelectric crystals 252
may also be mounted on the member 228. Crystals 252 act
as sensors and provide an electrical feedback signal on
line 254 which is proportional in frequency and amplitude
to the frequency and amplitude of the acoustic waves
traveling through the member 228. The feedback signal on
line 254 may be used by the driver circuit 240 to control
the frequency and amplitude of the drive signal applied on
lines 236 and 238.
Fig. 13 illustrates a fifth embodiment of the
present invention in which the elements corresponding to
the those in the fourth embodiment have been designated by
the same numerals as those used in Figs. 10-12. The
stimulator member 228 of Fig. 13 is rectangular in
cross-section and is substantially 1/2 wavelength long,
that is, L equals 1/2~ . Piezoelectric crystals 232 and
234 (not shown~ are mounted on opposing faces of the
member 228.
A vibration transmission pin 256 is mounted on
one end of the member and is preferably pressed into a
hole in the end of the member or is machined on the end of
the member. The pin 256 directly transmits the movement
of the lower end of the member 228 to the orifice plate
222. The pin 256 has a cross-sectional area, taken in a
plane substantially perpendicular to the direction of the
elongation of member 228, which is substantially less than
the cross-sectional area of the member. Thus, the acoustic
waves in the member 228 do not pass through pin 256, but
rather are reflected back toward the nodal plane which
passes through pins 248. The length of pin 256 is not
related to the frequency o~ operation of the stimulator
07~
MDF 068 P2 -25-
means, since the pin acts merely as a means of transmitting
the vibrations from the anti-node at the end of member 228
to the plate 222. The pin 256 passes through opening 244
and is engaged by a small diameter O-ring 258 which
prevents leakage of fluid from reservoir ~16. Preferably,
an automatic gain control in the driver circuit allows the
stimulation amplitude to be held constant, regardless of
the degree of damping provided by O-ring 258.
A single piezoelectric transducer 260 is mounted
ln on a side of the member 228 other than the sides upon which
the piezoelectric transducers 232 and ~34 are mounted.
Transducer 260 provides a feedback signal on line 254 which
may be used by a driver circuit to control operation of
the stimulator.
It will be appreciated that in each of the above
described embodiments of the invention there are provided
surface mounted transducers which induce shear stresses
therebelow. These shear stresses are converted to compres-
sion waves which in turn are coupled into the fluid
filaments.
While the method and the forms of apparatus
herein described constitute preferred embodiments of this
invention, it is to be understood that the invention is
not limited to such precise method or forms of apparatus,
and that changes may be made therein without departing
from the scope of the invention which is defined in the
appended claims.
The embodiments of the invention in which an
exclusive property or privilege is claimed are defined as
follows:
